Photoluminescence characterization of pure and Sm3+-doped thin metaloxide films

Photoluminescence (PL) of pure and Sm3+-doped TiO2, ZrO2 and HfO2 thin films were studied in the temperature range of 6– 300 K. The thin (100–250 nm) films were prepared by using both the atomic layer deposition (ALD) technique and the sol–gel spin-coating process. The ion implantation was applied to dope the ALD-grown films with Sm3+ ions, whereas an in situ doping was used in the sol–gel process. The PL was excited via band-to-band transitions by using several pulsed lasers as well as tuneable synchrotron radiation in the energy range of 4–20 eV. PL excitation spectra and decay kinetics were recorded. The dominating intrinsic emission of undoped materials was attributed to the radiative recombination of self-trapped excitons (STE). In doped materials, a broadband emission superposed by Sm3+ emission lines of a well-pronounced fine structure was observed under laser excitation. The broadband emission was attributed to the recombination of various bound excitonic states. The PL excitation spectra of doped and undoped films showed different behaviour, which was attributed to the damage produced by ion implantation and uncontrolled impurities incorporated into the films in sol–gel process. Relaxation of electronic excitations and the energy transfer process to Sm3+ ions is discussed.